Radiative Transfer in Galactic Environments with Clumpy Dust

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Session 35 -- ISM: Abundances and Dust
Display presentation, Wednesday, June 14, 1995, 9:20am - 6:30pm

[35.11] Radiative Transfer in Galactic Environments with Clumpy Dust

K.\ D.\ Gordon \& A.\ N.\ Witt (U. of Toledo)

The interstellar medium (ISM) in both our Galaxy and in other late-type galaxies has an inhomogeneous or clumpy structure. Using Monte Carlo techniques, we have investigated the affects of this clumpy structure on the radiative transfer in different galactic environments. These galactic environments include those dealt with in Witt, Thronson, \& Capuano (1992, ApJ, 393, 611) with the added dimension of a two phase dust structure described by the total amount of dust, the filling factor of the high density clumps, and the density ratio between the high and low density phases of the ISM. In addition, the parameters describing the dust properties (the albedo and scattering phase function asymmetry) have been compiled from the most recent Galactic observations from the IR to the UV. The resulting attenuation curves show a wide range of behavior, including a reduction in the strength of the 2175 \AA\ bump and an overall flattening of the slope. The reddening vectors for various colors are nonlinear and, usually, have a maximum value after which they return to their nonattenuated colors or even to bluer colors. From this result, the structure of the ISM in a galaxy may be determined from its integrated colors. We also deduce the total attenuation in spiral disks at V is more a function of the structure than a function of the total amount of dust and normally does not exceed 1--2 magnitudes. Using an assumed spectral energy distribution, the calculated $F_{IR}/F_{OPT}$ indicates the ISM in ultra-luminous interacting galaxies has a more homogeneous structure than the ISM in noninteractive galaxies.

This work was supported by NASA through LTSA Grant NAGW-3168 to The University of Toledo.

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